The present invention relates to a product assembly system and method of assembly. More particularly, this invention concerns a production line manufacturing system and method for building automotive vehicle bodies wherein a succession of workpieces is moved past stationary work stations. This invention is also concerned with a programmable multi-position rotate unit that can be used in each of the work stations to accommodate both changes in workpieces to be processed and tools.
Assembly systems for welding together automotive vehicle bodies by programmable robots and which provide respot or finish welding at successive welding stations are known. These assembly systems typically include a carrier which transfers a succession of workpiece holding pallets along a route passing through one or more framing welding stations. Each framing welding station typically includes a programmable robot to perform the welding operations and to preassemble a "body in white" from workpieces. Exemplary of an asynchronous assembly system is U.S. Pat. No. 4,928,383 of the inventors herein, the disclosure of which being specifically incorporated herein by reference.
One disadvantage with some of the previous assembly systems is that the work stations did not allow the user to verify, measure, and update data for fixturing, tooling, workpiece conditions and machining results and then react to this data in a fully automatic mode. Further, changing the model mix was not always totally flexible and resulted in some downtime. Desirably, the work station would include a platform which is rapidly replaceable to accommodate model mix.
Previous systems utilized palletized work stations, wherein each subassembly is built upon a different tooling pallet (e.g., a carousel turntable, automatically guided vehicle, palletized conveyors) which while flexible, did not assure repeatability. It would be desirable to have flexibility of processing different parts in a single line with each station being programmable.
An object of the present invention is to provide an assembly system such as for welding vehicle bodies and a flexible work cell therefore. A work cell in accordance with this invention has flexibility, whereby to change part loading frames easily and which can stop almost instantaneously.
An object of this invention therefore is a manufacturing process which can accommodate model mix and be quickly retrofitted to run prototype parts without interrupting current production, transport a plurality of parts to be worked on in an asynchronous manner along a single endless line between a series of work stations, and perform a sequential variety of operations on the parts, each work station being programmable, to select an operation to be performed, including performing no operation at all, whereby to expose the parts to a fraction of the operating capacity of the line.
Briefly stated, to accomplish the foregoing objects, the present invention is directed to a vehicle body welding assembly system including at least one working cell and a carrier adjacent thereto for transporting vehicle bodies, such as vehicle side frames, to and from the working cell. The assembly system is expandable to include a plurality of like configured working cells, as needed, and serviced by the carrier.
The working cell comprises a permanently installed base and a four-position horizontally arranged fixture rotate table including four vertically arranged fixtures removably mounted thereon. A precision locator key on each of the fixtures positions each individual fixture on the rotate table and also serves as a positive fixture stop in the work position. A single gear wheel arranged horizontally is connected to the rotary table and has radially inwardly directed gear teeth which mesh with corresponding radial teeth on a motor drive to rotate the table in either direction, the gear and motor drive being centrally accessible and vertically replaceable and functioning with programmable control means to provide rapid braking. A pallet means is connected to the carrier and suspended vertically above the rotate table and brought into registration with a predetermined fixture. Depending on the model mix, the table may not have to rotate at all. A control for detecting the presence of a vehicle frame to be worked on controls the operation of the carrier and motor drive and cooperates to accurately position a desired fixture adjacent to the work position. The fixture stop makes contact with a programmable clamping means associated with the base and fixtures whereby the rotate table and a selected fixture are locked into a desired position.
Advantageously each fixture itself determines the final position, not the rotate unit. This results in a higher level of accuracy and repeatability than present systems. As a result, precise positioning or dimensional accuracy of the pallet is not required.
The work cell is multi-sided to include a four station arrangement but can advantageously be expanded into a five or six station.
Another advantage of the system herein is that a control system can be programmed for a given model mix and then be reprogrammed for a different model mix without programming each station independently.
Downtime is minimized because without interrupting current production, maintenance can be performed on stored idle tools and idle tools can be exchanged for model change.